1. Field of the Invention
This invention relates generally to load carrying structural members and in particular to a redundant rotor blade retention system having a passive secondary load path which becomes active in the event the primary load path fails. It is highly desirable that the major structural components of aircraft be provided with multiple load paths so that the likelihood of accidents will be minimized in the event of a structural failure of one of those components. The rotor blades of helicopters and other rotor craft must be secured to the rotor hub in such a manner so as to permit rotation of the blade about a pitch axis. Rotation of the blade about its pitch axis is necessary in order to properly control the aircraft. It is for this reason that any redundant or secondary load path for connecting a rotor blade to a hub should include means for permitting the rotor blade to be rotated abouts its pitch axis.
2. Description of the Prior Art
Rotor blade retention systems which provide a secondary load path are known in the prior art. Many of the prior art systems have been complex and expensive to manufacture. While some of the prior art systems have provided a secondary load path capability they have not permitted the blade to be rotated about its pitch axis when the primary load path fails. Some of the prior art systems fail to lubricate a secondary load path thereby resulting in the limited use thereof.
U.S. Pat. No. 3,942,910 issued Mar. 9, 1976 to Snyder discloses a redundant system for attaching a blade to a helicopter rotor. This system provides a redundant centrifugal load supporting system which allows pitch adjustments of the blade upon failure of the primary load carrying system. It is, however, substantially different from the present invention.
U.S. Pat. No. 2,600,531 issued June 17, 1952 to Hafner suggests, but does not disclose in the drawings, a redundant secondary load path which will carry centrifugal loads. However, no redundancy is provided with respect to enabling the blade to be rotated about its pitch axis.